1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor having chip part such as a capacitor arranged near a semiconductor element and a heat radiation member such as a heat spreader attached to such a semiconductor device.
2. Description of the Related Art
In recent years, a semiconductor element has become being operated at a higher frequency, and an amount of heat generated during operation has increased. In order to cool the semiconductor element by radiating heat from the semiconductor element, a heat spreader as a heat radiation member is provided to a backside of the semiconductor element mounted on a substrate in many cases. In order to radiate heat efficiently, a heat spreader is formed to have an outer configuration larger than that of the semiconductor element so as to cover the entire semiconductor element. Then, the heat spreader is bonded to the backside of the semiconductor element by a heat transfer bonding material
FIG. 1 is a cross-sectional view of a semiconductor device having a conventional heat spreader. As shown in FIG. 1, a semiconductor element 1 is mounted on a printed circuit board 2, and a heat spreader 3 is provided to cover the semiconductor element 1. The heat spreader 3 has a leg part 3a which extends to the printed circuit board 2, and a concavity 3b is formed so as to accommodate the semiconductor element 1 therein.
Chip parts (electronic parts) 4 such as a capacitor are mounted on the printed circuit board 2 in a surrounding area of the semiconductor element 1. Thus, the concavity 3b of the heat spreader 3 is formed in a size which can also accommodate the chip parts 4.
The heat spreader 3 is formed by a metal having excellent heat transfer property such as, for example, copper (Cu), and is bonded to the backside of the semiconductor element 1 by a bonding material 5. As for the bonding material 5, although a heat transfer resin, which is a resin added with heat transfer particles, may be used, a metal bonding material such as a solder or a silver paste has become used so as to further improve the heat transfer property.
A surrounding portion of the concavity 3b of the heat spreader 3, that is, an end surface of the leg part 3a is bonded to the printed circuit board 2. Thereby, the heat spreader 3 is fixed to the printed circuit board 2, and an effect that the printed circuit board 2 is reinforced by the heat spreader 3 is obtained.
If a solder, which is a metal bonding material, is used as the bonding material 5, the heat spreader 3 is placed and temporarily fixed on the printed circuit board 2 in a state where the solder is inserted between the backside of the semiconductor element 1 and a bottom surface of the concavity 3b of the heat spreader 3. The thus-assembled printed circuit board 2 and the heat spreader 3 are put in a reflow furnace and heated to melt the solder, and, thereafter, the melted solder is solidified.
When reflowing the solder as the bonding material 5, if an amount of the solder is excessive, the melted solder may be extruded from the backside of the semiconductor element 1 as shown in FIG. 2. Additionally, when a pressure is applied to the melted solder and an oxide film on the surface of the melted solder is broken, solder particles may scatter from the broken point of the oxide film. In such a case, the extruded solder or scattered solder may contact the chip parts 4 arranged near the semiconductor element 1, which may result in short-circuiting of the chip parts 4.
In order to solve such a problem, there is suggested a technique to cover the chip parts 4 by an under-fill 6, which is filled between the semiconductor element 1 and the printed circuit board 2, by supplying a generous amount of the under-fill 6 (for example, refer to Patent Documents 1 and 2).
Patent Document 1: Japanese Laid-Open Patent Application 2000-200870
Patent Document 2: Japanese Laid-Open Patent Application 2001-267473
As mentioned above, the under-fill 6 filled between the semiconductor element 1 and the printed circuit board 2 is supplied as a liquefied resin having a relatively low viscosity. Thus, even if the under-fill 6 is supplied so as to cover the chip parts 4, there may be a case where the chip parts are not covered completely. Additionally, if many chip parts 4 are arranged, it takes time and effort to supply the under-fill 6 since the under-fill 6 must be supplied to each of the chip parts 4. Moreover, since a large amount of the under-fill 6, which is relatively expensive, must be used, there is a problem that the manufacturing cost of the semiconductor device is increased.
Additionally, if the under-fill 6 is supplied after the chip parts 4 are soldered and when electrodes of opposite ends of each chip part 4 are soldered, there may be many cases where a narrow air gap (indicated by a reference numeral 7 in FIG. 2) is formed between the bottom of the chip part 4 and the printed circuit board 2. If the under-fill 6 is supplied to the chip parts 4 after the chip parts 4 are soldered in the above-mentioned state, there may be a case where the under-fill 6 cannot enter the air gap and the air gap cannot been filled by the under-fill 6.
In such a case, when the semiconductor device is heated in a reflow furnace so as to melt the bonding material 5 to bond the heat spreader 3, the solder on the opposite ends of the chip part 4 is also temporarily heated. At that time, the melted solder may flow into the air gap under the chip part 4 since the upper side of the chip part 4 is covered by the under-fill 6. In such a case, there is a problem in that electrodes on opposite ends of the chip part 4 are short-circuited.